[argyllcms] some questions for using targen

  • From: Michael Schulz <ms.typografik@xxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Mon, 27 Sep 2010 19:07:22 +0200

Hi,

it's quite a while ago I had the discussion below about using targen for
proofing purposes. At that time I didn't understand Nikolay's advice and I'm
not sure that I understand it now. But I would like to ask people more
familiar with Argyll if I'm right or wrong when I think this was meant:
(excuse my bad English)

1. print a target with OFPS - but with how many patches for a high quality
CMYK profile?
2. create a profile with a chosen black generation from the measured data
3. print a second target with "perceptual space body centred cubic grid
spread" by using the profile which was created before - but with how many
patches and with what kind of rendering intend (relative colorimetric or
absolute colorimetric with paper simulation)?
4. combine the measured data from the two targets and create the final
proofing profile

I think I've understand the advice to analyze the printers linearity - in my
opinion it's not too bad - see attached files (from ECI2002 target).

Thanks for putting some light in the dark
Michael Schulz


Am 12.10.2009 16:39 Uhr schrieb "Nikolay Pokhilchenko" unter
<nikolay_po@xxxxxxx>:

> Michael Schulz wrote:
> 
>> I would like to ask you and other people who have already experiences using
>> targen to create test target values for proofing purposes in practice, which
>> targen options you normally use.

> For CMYK printers:
> The "perceptual space body centered cubic grid spread" is computing on
> inverted profile table. The inverted profile table is depend of black
> generation selected. But black generation may be computed only on OFPS or
> "device space body centered cubic grid spread" data. So it is necessary to
> print OFPS (the best way) or "device space body centered cubic grid spread"
> target in any case.
> When the desired black generation selected and normal profile is built, the
> additional black-generation-depended target may be printed with "perceptual
> space body centered cubic grid spread". The advantage of perceptual space
> spreaded target (based on normal profile) will be the patch placement only by
> selected black generation, not in all device space. Being combined with
> previous *.ti3 data it may significant improve the next profile quality (with
> the same black generation) exact in needed device space areas.
> 
>> I'm talking about the default option (OFPS) - with the result of mostly dark
>> patches, the -R option which gives patches with a perceptual space
>> distribution and the -c option using a previous profile.
> 
> OFPS, -r and -i will produce the close results. They generally dark because of
> subtractive CMYK print principle. The device space spread will produce many
> ink combinations and many of combinations really must be dark. It is necessary
> to print all of device space combinations for correct black generation
> computing.
> The one of a problems may be the printer linearity problem. Try to build
> preliminary profile (about 600 patches) and evaluate CMY linearity with zero
> and default black generation:
> 
> xicclu -ir -fif -pl -b -g -kz Preliminary.icc
> xicclu -ir -fif -pl -b -g -kr Preliminary.icc
> 
> Alalyze the graphs and conclude if the printer linear. It may be very
> important. In several non-linear cases the targets with OFPS may be extremely
> dark and even they reading by instrument may became a problem. The instrument
> may don't distinct the margins between patches on such targets.
> So the best results will be with linearized printer.
> 
> Good Luck!

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